1. Field of the Invention
The present invention relates generally to the field of hydrogen storage with metal hydride based hydrogen storage alloys, and in particular to a device for charging and activating the hydrogen storage alloys contained in canisters.
2. Description of the Prior Art
Hydrogen is the most abundant element in the universe and can be a great energy source. However, due to the low density of hydrogen gas, storage of hydrogen is a challenge to the hydrogen energy industry. A variety of ways are currently available for storage of hydrogen. For example, hydrogen can be stored in a compressed gas form. Compressing hydrogen is an expensive process and the compressed hydrogen gas still occupies a great amount of space. In addition, the high pressure of compressed hydrogen is adverse to operation safety.
Hydrogen can also be stored in liquid state. However, liquid hydrogen must be stored under cryogenic temperature. A great amount of energy is required to maintain the extreme low temperature. Also, continuously venting is a safety issue to be concerned.
One of the most feasible ways for economically storing hydrogen is hydride form. Metal hydrides, which are formed by metallic materials commonly referred to as hydrogen storage alloy, are employed to absorb and hold a great amount of hydrogen at room temperature. Some of the hydrogen storage alloys can store hydrogen at a higher density than pure hydrogen, which make them economically advantageous.
The hydrogen storage alloys are commonly deposited in a container or a canister and is activated by charging hydrogen into the canister. Once a hydrogen storage canister is fabricated, the hydrogen storage alloy contained therein must be activated by repeatedly charging and releasing hydrogen. A similar process is also adopted to restore the capacity of poisoned hydrogen storage alloy, which is caused by absorption of impurity, by the metal hydrides.
Once the hydrogen held in the hydrogen storage canister exhausts, the canister has to be recharged with hydrogen. This is usually done by refilling hydrogen into the canister, causing the hydrogen storage alloy to take up the hydrogen. Since a variety of metal hydrides are available for storage of hydrogen, different charging conditions are required for recharging hydrogen storage canister made of different metal hydrides. Among the known metal hydrides, LaNi based metal hydrides, FeTi based metal hydrides and Mg based metal hydrides are most commonly used in powering electrical vehicles.
In recharging the hydrogen storage canister, a high hydrogen pressure and a predetermined flow rate of hydrogen must be maintained in order to achieve desired charging result. In addition, the hydrogen storage alloy releases heat when it absorbs hydrogen. The heat must be properly removed in order for the alloy to continuously take up hydrogen to the maximum capacity thereof. The rate at which the hydride alloy absorbs hydrogen is dependent upon the rate at which the heat is removed from the alloy. On the other hand, when the hydrogen storage alloy releases hydrogen, it absorbs heat, causing drop-down of temperature. To ensure proper release rate of hydrogen from the alloy, the alloy must be maintained at a suitable operation temperature by internal or external heating.
In addition to the requirements for charging and discharging hydrogen discussed above, a commercial hydrogen charging device must have a structural strength sufficient to support a number of hydrogen storage canisters, which may be weighted 4–5 Kg each, in order to charge the canisters efficiently. Cooling and heating the canisters inside the charging device is also an important concern for efficient charging process. To be even more efficient, quick connectors for connecting the canisters to a hydrogen supply source are also required in a commercial charging device. All these are heretofore not available in any commercial device or machine for efficiently charging hydrogen storage canisters.
For safety and effectiveness purposes, evacuation of impurity gas from the canisters and filling of inertial gas during leakage of hydrogen are also required for a commercial charging machine. Still, these requirements are not met by any known and market available commercial hydrogen recharging machines.
It is thus desired to provide a device for charging and activating hydrogen storage canister made of metal hydrides that eliminates the above deficiencies.